Low-alloy high-yield strength weldable steel



Patented Feb. 19, 1952 UNITED STATES PATENT OFFICE 2,586,042 Low-littoyriion-yiniln STRENGTH WELDABLE STEEL John M. Hodge and Richard D. Manning, Pittsburgh, Pa., assignors to United States Steel Company, a corporation of New Jersey No Drawing. Application April 8,1951, Serial No. 219,772

2' Claims; 1

This invention relates to an improved low-- alloy steel characterized by high strength combined with superior toughness and weldability in the quenched and tempered condition.

Low-alloy, high-strength steels have many applications in the manufacture of heavy machinery, trucks, railroad cars, ships, etc, which are frequently fabricated by welding. The steels heretofore available for these purposes have been generally limited to yield strengths of 50,006 p. s. i. or, in sections larger than inch in thickness, to even lower strength levels. The improved steel of this invention, on the other hand, can readily be heat treated to yield strengths of 100,000 p. s. i. and higher. Together with this high strength, our new steel can be safely welded without preheating or' other special precautions and, furthermore, will exhibit superior toughness welded or unwelded and will retain this toughness at lower temperatures than the lower strength steels which were previously used for welded construction. The combination of elements in our invention is unique in that it permits the attainment of a microstructu're consisting mainly of low-carbon tempered mart'ensite after heat treatment with relatively low percentages of alloying elements and without the poor 'weldability characteristic of prior art steels used at these high-strength levels.

This unique combination of properties is obtainable by forming the steel of the following elements and ranges thereof:

- Range, per cent Balance iron and other elements in residual amounts.

Copperoptional but preferred since amounts between 0.'20.5% aid corrosion resistance.

Within these composition limits, the characteristic properties of yield strengths of 90,000 p. s. i. minimum together with Keyhole Charpy impact values of 15 foot pounds at temperatures down to as low as --150 F. and excellent weldability can be obtained with the hereinafter de- .2 scribed heat treatment, in plate sizes from to 4 inches in thickness or in corresponding section sizes in other shapes.

The high degree of hardenability of the steels of the present invention results from the proportion of carbon, manganese, nickel, chromium, molybdenum and boron as recited. In so far as hardenability is concerned, boron intensifies the effects of the above alloying ingredients permitting smaller amounts of these elements to be used than formerly. In addition, the inclusion of the small amount of boron results in an unusual increase in the weldability of the compositions. This effect is shown by the following weld-test data on the following steels:

COMPOSITIONS Steel A Steel B Steel 0 Per cent Per cent Per cent 7 Carbon Q. 14 0. 15 0. 15 Manganese 0. 82 0. l. 00 Nickel 0. 91 O. 88 0. 87 Chromium 0.61 0.59 0. 52 Molybdenum 0. 48 0. 50 0. 47 Vanadium 0. 05 0. 09 0. 07 Boron 0. 005 0. 0038 None Silicon 0. 23 0. 20 0. 46 Copper 0.33 0. 29 0. 30

One (1") plates were rolled from commercial heats of the above analyses and subjected to Weld tests of the Batelle type using standard electrode E-6010. The plates were water quenched from 1650 to 1700 F. and tempered at 1200 F. The welding was conducted at several temperatures and without preheating or postheating. Both automatic and manual methods were used. The samples were examined by Magnaflux methods for under bead cracking. The results are tabulated below:

The marked improvement due to the boron is readily apparent from the foregoing table and is further evidenced by notch bend tests, the results of which are given in the following Table II:

Table II Transition Temperature 1 Steel Steel A Steel B (No Boron) Material before welding. Welded material 112F 107F -78F 1 Temperature below which material showed amarked decrease in ductility.

2 Below-l43 F.

It is apparent from these results that the steels of the present invention can be welded and retain a remarkable degree of ductility not obtainable with other compositions. Moreover, tensile tests on butt-welded specimens broke outside the weld, indicating that the full strength of the base material was retained in the Welded condition.

The foregoing improvement in weldability is obtained without sacrifice of hardenability. In fact a considerable increase in hardenability is achieved by the boron containing compositions of the present invention as shown by the following Table III:

! Distance from quenched end in sixteenths of an inch.

It will be noted that the point at which the micro-structure of the specimens exhibited less than 95% martensite occurred at about 17/16 for the boron containingsteel A and at about /16 for the steel C whichcorresponds to an ideal diameter D1 of 4.5 and 3.3 inches respectively. This clearly indicates the higher hardenability attributable to the composition of our invention.

The following Table IV indicates the other desirable mechanical properties of our steel.

Table IV 2 in a e; 1 4 r0 e r0 e Material Tested plate plate Longitudinal Longitudinal Treatment:

Water quenched, F 1, 650 1, 650 Tempered, F 1, 200 1,200 0.2% ofiset Yield Strength p. s. in 118,000 112, 000 Tensile Strength, p. s. i 125, 000 122,600 Elongation in 2", Per Cent 39. 7 42. 7 Reduction in Area, Per Cent 59.6 65. 5 Keyhole Charpy Impact Ft 5.,

Room Temp 0 F 45 l F 25 200 F 26 While we have shown and described a specific embodiment of our invention, it will be understood that this embodiment is merely for the purpose of illustration and description and that various other forms may be devised within the scope of our invention, as defined in the appended claims.

We claim:

1. A low-alloy, high-strength steel, characterized by good weldability and toughness, when heat treated by cooling sufiiciently rapidly from an austenitizing temperature to obtain a martensitic microstructure and thereafter tempering at temperatures over 1100 F., said steel comprising from .10 to .20% carbon, .60 to 1.00% manganese, .70 to 1.00% nickel, .40 to .80% chromium, .40 to molybdenum, .03 to .10 vanadium, .002 to .006% boron, .15 to 35% silicon, .0 to .50% copper, balance iron and residual amounts of other elements.

2. A low-alloy, high-strength steel having a tempered martensitic microstructure resulting from rapidly quenching it and thereafter tempering at temperatures above 1100 F., said steel being characterized by good weldability without preheating or postheating and toughness, said steel comprising about .10 to .20% carbon, .60 to 1.00% manganese, .70 to 1.00% nickel, .40 to .80% chromium, .40 to molybdenum, .03 to .10% vanadium, .002 to 006% boron, .15 to 35% silicon, .0 to .50% copper, balance iron and residual amounts of other elements.

JOHN M. HODGE. RICHARD D. MANNING.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,478,420 Payson Aug. 9, 1949 2,528,867 Day Nov. '7, 1950 OTHER REFERENCES Transactions of the American Society for Metals, vol. 40, 1948, pages 1102 to 1104, published by the American Society for Metals, Cleveland, Ohio. 

1. A LOW-ALLOY, HIGH-STRENGTH STEEL, CHARACTERIZED BY GOOD WELDABILITY AND TOUGHNESS, WHEN HEAT TREATED BY COOLING SUFFICIENTLY RAPIDLY FROM AN AUSTENITIZING TEMPERATURE TO OBTAIN A MARTENSITIC MICROSTRUCTURE AND THEREAFTER TEMPERING AT TEMPERATURES OVER 1100* F., SAID STEEL COMPRISING FROM .10 TO .20% CARBON, .60 TO 1.00% MANGANESE, .70 TO 1.00% NICKEL, .40 TO .80% CHROMIUM, .40 TO 60% MOLYBDENUM, .03 TO .10 VANADIUM, .002 TO .006% BORON, .15 TO .35% SILICON, .0 TO .50% COPPER, BALANCE IRON AND RESIDUAL AMOUNTS OF OTHER ELEMENTS. 